1. Field of the Invention
The invention relates to a conductive adhesive agent used in joining of an electronic element and a printed-circuit board in a field of packaging of the electronic element, a packaging structure using the conductive adhesive agent, and a method for manufacturing the packaging structure.
2. Description of the Related Art
Recently, high consciousness for environmental harmonies has started to restrict use of lead contained in a solder alloy in the field of packaging of electronic devices, thus leading to an emergent need for establishment of technologies of joining electronic elements using a material in which lead is not contained.
As a lead-free packaging technology is known the one using a lead-free solder and a conductive adhesive agent. Recently, however, more and more attention is attracted to a conductive adhesive agent expected to have merits such as flexibility of a joining portion and lower packaging temperature.
A conductive adhesive agent generally has conductive particles dispersed in a resin-based adhesive component. To package a device, first a conductive adhesive agent is applied on a board electrode, the device is attached thereon, and then the resin is hardened. By this process, the joining portions are adhered to each other by the resin and also the conductive particles come in contact with each other as the resin shrinks, thus ensuring continuity at the joint.
The resin of a conductive adhesive agent has a hardening temperature of about 150xc2x0 C., which is very low as compared to a melting temperature of about 240xc2x0 C. required for soldering, thus qualifying that agent for use even in packaging of such inexpensive devices that have a low heat resistance.
Also, the joining portions are adhered to each other by a resin, thus being able to flexibly accommodating a deformation due to heat or an external stress. This gives the conductive adhesive agent a merit that the joining portions adhered thereby is not liable to have cracks as compared to those adhered by solder which is an alloy.
For the above reasons, the conductive adhesive agent is expected as an alternative of solder.
Silver, generally used as conductive particles of a conductive adhesive agent, has such a characteristic that it is subject to easy ion migration or sulfurization, problem of which must be solved to put the conductive adhesive agent to practical use as an alternative material for solder.
First, ion migration is described as follows. A phenomenon of ion migration is a sort of electrolytic action, by which dielectric breakdown occurs between electrodes along the following four steps when an electrolyte such as water is present between the electrodes under application of voltage:
Step 1: An anode metal is eluted and ionized;
Step 2: The ionized metal migrates toward a cathode under application of voltage;
Step 3: The metal ions which have migrated to the cathode are precipitated; and
Step 4: Steps 1 through 3 are repeated.
Such a phenomenon of ion migration causes the metal to grow in a tree shape between the electrodes, finally bridging the gap between the electrodes, resulting in dielectric breakdown.
Silver used as a conductive filler of a conductive adhesive agent is easily eluted, thus bringing about ion migration. Further, a recent trend for further reduction in size and weight of electronic equipment has narrowed a pitch between electrodes formed in a semiconductor device an electronic element or on a printed-circuit board, thus further easily causing ion migration. Taking this into account, the problem of ion migration must be solved indispensably to put to practical use the packaging technology by use of a conductive adhesive agent.
There have conventionally made such three proposals that inhibit ion migration:
Proposal 1: Alloying of conductive filler (e.g., alloying of silver and copper or silver and palladium);
Proposal 2: Sealing of conductive adhesive agent by use of insulating resin such as epoxy resin; and
Proposal 3: Capturing eluted metal ions and rendering them insoluble material by addition of ion capturing agent such as ion exchange resin or chelating agent to conductive adhesive agent
Those proposals, however, have the following disadvantages. Proposal 1 requires a very expensive filler metal, thus increasing a cost of the conductive adhesive agent. Proposal 2 needs to add an extra step of sealing to thereby increase the number of required steps or greatly expand provisions, thus increasing the manufacturing costs. Proposal 3 causes a metal ion to be eluted from the conductive filler to thereby deteriorate contact-ness of the conductive filler, thus raising the connection resistance.
Thus the above-mentioned proposals have indeed an effect of inhibiting ion migration but also have various problems and so are difficult to put to practical use except in a special application field.
Next, a phenomenon of sulfurization is described as follows. Sulfurization refers to such a phenomenon that a metal reacts with a weal acidic air containing a sulfuric content such as hydrogen sulfide or sulfur dioxide to provide such a material with low conductivity that is called a metal sulfide. Although sulfurization is not know enough yet, it is considered to occur along the following steps:
Step 1: A metal is eluted and ionized in a weak acidic atmosphere; and
Step 2: the metal ions react with sulfur ions to generate a metal sulfide.
As described above, a conductive filler is mainly made up of silver but is liable to be sulfurized, so that when silver is sulfurized, volume-specific resistance of the conductive adhesive agent rises, which is accompanied by a rise in the connection resistance. Few solutions for this problem have been reported so far, so that a packaging structure using a conductive adhesive agent cannot be applied to a product having an electronic element which may be used in such an environment as surroundings of a hot spring or volcano, in which hydrogen sulfide or sulfide dioxide is present at a relatively high concentration. This greatly restrict application fields of the packaging structure using a conductive adhesive agent.
In view of the above, it is an object of the invention to provide such a packaging structure using a conductive adhesive agent that is capable of maintaining a reliability even under a very humid condition or such a severe condition as a gaseous atmosphere containing sulfur.
To this end, a conductive adhesive agent according to the invention has a binder resin, a conductive particle, and an elution preventing-film forming agent, which forming agent becomes reactive after electrical continuity through the conductive particle is established in this conductive adhesive agent when the binder resin is hardened, thus forming an elution preventing film on the surface of the conductive particle. This causes the following to occur.
When the surface of the conductive particle is coated with the elution preventing film, the conductive particle can be prevented from being eluted even if it is left in a hot and humid environment or in a gas containing sulfur. Therefore, the elution preventing film can prevent ion migration as well as the above-mentioned first step of sulfurization. Thus, the conductive adhesive agent according to the invention can be used to manufacture a packaging structure not liable to encounter ion migration and sulfurization.
When, in this case, the elution preventing film is made of an insulating material and if it is present at a site related to conduction (i.e., contact point between conductive particles and that between a conductive particle and an electrode or the like), it inhibits electrical continuity, thus leading to such a disadvantage that raises a connection resistance of the packaging structure.
By the conductive adhesive agent according to the invention, on the other hand, no elution preventing film is formed on the conductive particle until that adhesive agent is hardened, so that only after the conductive particles come in contact with each other in the process of hardening, the elution preventing film is formed on the particle surface. Accordingly, the elution preventing film is not formed at a site related to continuity, thus avoiding a rise in the connection resistance.
If the above-mentioned requirement of the invention is not met, on the other hand, the object of the invention cannot be realized. That is, when an elution preventing film is formed on the conductive particles before continuity is established, that is, before the agent is hardened, the elution preventing film is already present at a site related to continuity when the conductive adhesive agent is hardened to thereby inhibit electrical continuity, thus raising the connection resistance.
For the conductive adhesive agent according to the invention, preferably the reactive temperature of the elution preventing film-forming agent satisfy the following conditions:
application temperature of conductive adhesive agent less than reactive temperature of elution preventing-film forming agent; 
and
reactive temperature of elution preventing film-forming agentxe2x89xa6hardening temperature of binder resin. 
When these conditions are established, the following will occur.
No elution preventing film is formed when a conductive adhesive agent according to the invention is applied. When the conductive adhesive agent starts to be heated to its hardening temperature, the elution preventing film-forming agent becomes reactive at a temperature range before the hardening to thereby form an elution preventing film on the conductive particle. At this point in time, the binder resin is not hardened yet so does not inhibit the formation of the elution preventing film. Therefore, the elution preventing film is formed uniformly everywhere on the conductive particle surfaces except on a contact point between the conductive particle and any other conductive substances (any other conductive particles or electrodes). When the elution preventing film is formed and then the conductive adhesive agent is heated up to its hardening temperature, the binder resin is hardened to complete connective fixation by the conductive adhesive agent.
Also, for the conductive adhesive agent according to the invention, the elution preventing film-forming agent contains a chelating agent, which preferably becomes reactive after electrical continuity through the conductive particles is established in this conductive adhesive agent when the binder resin is hardened, thus forming an elution preventing film containing a metallic complex on the conductive particle. Then, the following will occur.
Since the elution preventing film-forming agent contain a chelating agent, an elution preventing film containing a very stable material of metallic complex is formed on the conductive particle. Accordingly, even if a connection site given by the conductive adhesive agent is left in a hot and humid environment or in a gas containing sulfur, the conductive particle is not eluted.
Also, if a metallic complex, which is an insulating material, is present at a site related to continuity (contact point between conductive particles or between a conductive particle and an electrode), the electrical continuity is inhibited, thus raising the connection resistance of the packaging structure. As for a conductive adhesive agent according to the invention, on the other hand, no metallic complex is formed on the conductive particle before the conductive adhesive agent is hardened, so that only after the conductive particles come in contact with each other to establish continuity in the hardening step, the elution preventing film containing the metallic complex is formed on the particles. Thus, the elution preventing film containing a metallic complex is not formed at the site related to continuity, thus avoiding a rise in the connection resistance.
Also, to contain a chelating agent in an elution preventing film-forming agent for the conductive adhesive agent according to the invention, preferably the activation temperature of the chelating agent satisfies the following conditions:
application temperature of conductive adhesive agent less than activation temperature of chelating agent; 
and
activation temperature of chelating agentxe2x89xa6hardening temperature of binder resin. 
Then, the following will occur.
A chelating agent is a material which selectively reacts with a metal to form a metallic complex, which reaction is most liable to occur at an activation temperature of the chelating agent. Since the activation temperature is higher than an application temperature of the conductive adhesive agent and equal to or lower than a hardening temperature of the binder resin, it reacts with a metal at a temperature therebetween to thereby form an elution preventing film containing the metallic complex on the conductive particles. Therefore, before the conductive adhesive agent is hardened, the chelating agent is dispersed in the conductive adhesive agent, so that an elution preventing film is little formed on the conductive particle. Then, in the hardening step, the chelating agent reacts with the conductive particle to form the elution preventing film containing a metallic complex on the particle surfaces. This elution preventing film provides a protecting film for the conductive particle, thus inhibiting ion migration and sulfurization. Also, the elution preventing film is formed after continuity is established, so that the elution preventing film (metallic complex) is hardly formed at a site related to continuity, thus suppressing a rise in the connection resistance.
An activation temperature (reaction temperature) here refers to a temperature at which a chelating agent and a metal react with each other most frequently, generally coming near the melting temperature. Note here that the relation between the reaction between a chelating agent and a metal and the temperature is nonlinear in that at the activation temperature, the reaction is rapidly activated and at a temperature far distant from that, the reaction occurs little.
An application temperature of the conductive adhesive agent refers to a working temperature at which the conductive adhesive agent is applied on a board electrode by printing or using a dispenser in order to manufacture a packaging structure. The application temperature generally comes near room temperature of 20-40xc2x0 C. or so.
If as the chelating agent is employed such a material that has an activation temperature higher than the hardening temperature of the binder resin (e.g., bismthyol II having a melting temperature of 246xc2x0 C. as against a hardening temperature of 150xc2x0 C.), the chelating agent does not react with the conductive particle even after hardening, so that no metallic complex is formed, thus failing to obtain the effects of resisting against ion migration and sulfurization.
Since the activation temperature is often near the melting temperature, as the chelating agent may be used, for example, an anthranilic acid (melting point: 145xc2x0 C.), thionylide (217xc2x0 C.), or pyrogallol (132xc2x0 C.) as against such a conductive adhesive agent that has an application temperature of 25xc2x0 C. and a hardening temperature of 150xc2x0 C.
As for the conductive adhesive agent according to the invention, the elution preventing film-forming agent is encapsulated in a micro-capsule, so that preferably the melting temperature of this micro-capsule and the activation temperature of the chelating agent contained in the elution preventing film-forming agent satisfy the following conditions:
application temperature of conductive adhesive agent less than melting temperature of macro-capsule; 
melting temperature of micro-capsulexe2x89xa6hardening temperature of binder resin; 
and
activation temperature of chelating agentxe2x89xa6hardening temperature of binder resin. 
When those conditions are satisfied, not only the connection resistance of the packaging structure after hardening is inhibited but also more chelating agents can be selected. The reasons are explained below.
In this improvement, a chelating agent as encapsulated in a micro-capsule is added to the conductive adhesive agent to thereby inhibit the reaction of the unhardened chelating agent even more securely. The reasons are described as follows.
By the configuration according to the invention, the activation temperature of the chelating agent is higher than the application temperature of the conductive adhesive agent, so that the reactivity of the chelating agent is low before the binder resin is hardened yet. However, a water content, a hardening agent (amine, acid anhydride, or the like) a residual impurity given in production of a binder resin (chloride, or the like), or the like serves as a reaction accelerator, so that the chelating agent is actually reactive even before hardening, thus forming an elution preventing film containing a metallic complex on the conductive particle surfaces.
As for a conductive adhesive agent according to the invention improved as mentioned above, on the other hand, the chelating agent is protected in a micro-capsule, so that the chelating agent reacts little before the binder agent is hardened. When the binder agent starts to be hardened, the micro-capsule melts to thereby release the chelating agent, which then reacts with the conductive particle to thereby form an elution preventing film containing a metallic complex. Thus, by the invention improved as mentioned above, the elution preventing film (metallic complex) is further less formed before the binder resin is hardened, thus securely inhibiting a rise in the connection resistance in the conductive adhesive agent after hardening. Further, since the activation temperature of the chelating agent may well be lower than the application temperature of the conductive adhesive agent, the required properties (especially activation temperature) of the chelating agent become more lenient, thus enabling selecting more chelating agents that much.
As for the conductive adhesive agent according to the invention, preferably the elution preventing film-forming agent is made up of a water-insoluble material. Then, the following will occur.
Since the elution preventing film, once formed, does not solve out in a hot and humid environment, the in migration resistance is enhanced. The insoluble-ness is here defined that an insolubility (weight soluble in 100 g of water) is less than 1xc3x9710xe2x88x925 g.
As for a conductive adhesive agent according to the invention, preferably the elution preventing film-forming agent is made up of a material insoluble in a aqueous solution containing a hydrogen sulfide or sulfur oxide. Then, the following will occur. That is, since the elution preventing film, once formed, does not solve out in a weak acid aqueous solution or atmosphere containing sulfur, ion migration resistance and sulfurization resistance are enhanced.
As for a conductive adhesive agent according to the invention, preferably the elution preventing film-forming agent as dispersed in a non-polar solvent is added to this conductive adhesive agent. Then, the following will occur.
Since the non-polar solvent serves to inhibit the reaction of the chelating agent, in the conductive adhesive agent according to the invention improved as mentioned above, the chelating agent is reactive little before the binder resin is hardened. When the binder resin starts to be hardened, the chelating agent reacts with the conductive particle to thereby form an elution preventing film containing a metallic complex. Thus, by the invention improved as mentioned above, the elution preventing film (metallic complex) is formed further less before the binder resin is hardened, thus securely inhibiting a rise in the connection resistance in the conductive adhesive agent. Further, the activation temperature of the chelating agent may well be lower than the application temperature of the conductive adhesive agent, so that the required properties (especially activation temperature) of the chelating agent become more lenient, thus enabling selecting more chelating agents that much.
Also, to achieve the above-mentioned object, the packaging structure according to the invention includes an electric structure and a conductive adhesive agent layer formed on the electric structure in such a configuration that the conductive adhesive agent layer contains conductive particles and is coated with an elution preventing film except a contact point between these conductive particles and between the conductive particle and the electric structure.
This improves the ion migration resistance. This is because the elution preventing film, which provides a protecting film against ion migration, is formed on a necessary portion, that is, a portion except those related to continuity.
A packaging structure has another electric structure disposed on the above-mentioned one, so that these electric structures are electrically interconnected, the conductive adhesive agent layer has a very large effect on the connection resistance because of an ion migration reaction, or the like. To guard against this, the invention is applied to such a configuration so as to have a large effect.
In a packaging structure according to the invention, preferably the elution preventing film s made up of a material containing a metallic complex. Then, the following will occur. That is, since an elution preventing film containing a metallic complex, which is very stable in property, is formed on the conductive particle, the conductive particle does not solve out even if a site connected by the conductive adhesive agent is left in a hot and humid environment or in a gas containing sulfur.
Also, if a metallic complex, which is an insulating material, is at a site related to continuity (contact point between conductive particles or between a conductive particle and an electrode), electrical continuity is deteriorated, thus increasing the connection resistance of the packaging structure. A packaging structure of the invention as improved above, on the other hand, has no metallic complex formed at a site related to continuity, thus avoiding to increase the connection resistance.
In the packaging structure of the invention, preferably the elution preventing film is made up of a water-insoluble material. Then, the elution preventing film once formed dies not solve out even in a hot and humid environment, thus enhancing the ion migration resistance.
In the packaging structure of the invention, preferably the elution preventing film is made up of a material not soluble in an aqueous solution containing hydrogen sulfide or sulfur oxide. Then, the following will occur. That is, the elution preventing film once formed does not solve out even in a weak acid aqueous solution or an atmosphere containing sulfur, thus enhancing the ion migration resistance and the sulfurization resistance.
To manufacture such a packaging structure of the invention as mentioned above, the following two methods are available.
A first method prepares such a conductive adhesive agent that contains a binder resin, a conductive particle, and an elution preventing film-forming agent, a reaction temperature of which elution preventing film-forming agent satisfies the following conditions:
application temperature of conductive adhesive agent less than reaction temperature of elution preventing film-forming agent; 
and
reaction temperature of elution preventing film-forming agentxe2x89xa6hardening temperature of binder resin, 
the method comprising:
a conductive adhesive agent forming step of applying and forming the conductive adhesive agent on the electrode at the application temperature;
an elution preventing film-forming step of heating the conductive adhesive agent up to the hardening temperature and also permitting the elution preventing film-forming agent to react at the reaction temperature before that hardening temperature is reached to thereby form an elution preventing film on the conductive particle; and
a hardening step of heating the conductive adhesive agent up to the hardening temperature to harden the binder resin.
A second method prepares such a conductive adhesive agent that contains a binder resin, a conductive particle, and an elution preventing film-forming agent, reaction temperature of which elution preventing film-forming agent satisfies the following conditions:
xe2x80x83hardening temperature of binder resin less than reaction temperature of elution preventing film-forming agent,
the method comprising:
a conductive adhesive agent forming step of forming a layer of the conductive adhesive agent as unhardened on the electrode;
a hardening step of heating the conductive adhesive agent up to the hardening temperature to thereby harden the binder resin; and
an elution preventing-film forming step of re-heating the conductive adhesive agent to the reaction temperature or higher to thereby permit the elution preventing film-forming agent to be reactive, thus forming an elution preventing film on the conductive particle.
By those manufacturing methods, the following will occur.
That is, when a conductive adhesive agent according to the invention, no elution preventing film is formed. Then, when the conductive adhesive agent is heated to its hardening temperature, at a temperature before it is hardened, the elution preventing film-forming agent becomes reactive to thereby form an elution preventing film on the conductive particle. At this point in time, the binder resin is not hardened yet, thus avoiding inhibiting the formation of the elution preventing film. Therefore, the elution preventing film is uniformly formed everywhere on the conductive particle surfaces except on a contact point between the conductive particle and any other conductive materials (any other conductive particles or electrodes, or the like). Then, when the hardening temperature of the conductive adhesive agent is reached after the elution preventing film is formed, the binder resin is hardened, thus completing the connection fixation by the conductive adhesive agent.
By the second method, a rise in the connection resistance of the packaging structure can be inhibited further securely. The reason is as follows.
Since the reaction temperature of the elution preventing film-forming agent is higher than the hardening temperature of the binder resin, before the conductive adhesive agent is hardened and when it is being hardened, the elution preventing film-forming agent forms no elution preventing film on the conductive particle surfaces, thus providing good continuity. Then, the binder resin, after being hardened, can be re-heated up to a temperature higher than the reaction temperature of the elution preventing film-forming agent to thereby form an elution preventing film only at a site not related to continuity. Accordingly, the connection resistance of the packaging structure after hardening can be inhibited securely.
Also, preferably the first method prepares the elution preventing film-forming agent which contains a chelating agent, activation temperature of which satisfies the following conditions:
application temperature of conductive adhesive agent less than activation temperature of chelating agent; 
and
activation temperature of chelating agentxe2x89xa6hardening temperature of binder resin, 
during the elution preventing film forming step, the conductive adhesive agent being heated up to the hardening temperature so that at the activation temperature before that temperature is reached the chelating agent is made reactive to thereby form an elution preventing film containing a metallic complex on the conductive particle. Then, the following will occur.
The chelating agent selectively reacts with a metal to form a metal complex, which reaction occurs most at the activation temperature thereof. This improved manufacturing method uses a chelating agent and sets its activation temperature higher than the application temperature of the conductive adhesive agent and not higher than the hardening temperature of the binder resin. Accordingly, the chelating agent becomes reactive at a temperature between the application temperature of the conductive adhesive agent and the hardening temperature of the binder resin to thereby form an elution preventing film containing a metallic complex on the conductive particle. Therefore, before the conductive adhesive agent is hardened, the chelating agent is dispersed in the conducive adhesive agent, thus scarcely forming an elution preventing film on the conductive particle surfaces. When it starts to be hardened, the chelating agent reacts with the conductive particle to form an elution preventing film containing a metallic complex on the particle surfaces. This elution preventing film provides a protecting film for the conductive particle, thus inhibiting ion migration and sulfurization. Also, since the elution preventing film is formed after continuity is established, the elution preventing film (metallic complex) is hardly formed at a site related to continuity, thus suppressing a rise in the connection resistance.
Preferably the second method prepares the elution preventing film-forming agent which contains a chelating agent which has an activation temperature higher than the hardening temperature of the binder resin, in which:
At the hardening step, the binder resin is hardened by a heating process at a temperature lower than the activation temperature; and
at the elution preventing film forming step, the conductive adhesive agent is re-heated up to a temperature not less than the activation temperature to act with the chelating agent, thus forming an elution preventing film containing a metallic complex on the conductive particle. Then, it is possible to form the elution preventing film that contains a metallic complex.
Preferably the second method prepares the elution preventing film-forming agent that is encapsulated in a micro-capsule, so that the melting temperature of this micro-capsule and the activation temperature of the chelating agent containing the elution preventing film satisfy the following conditions:
application temperature of conductive adhesive agent less than melting temperature of micro-capsule; 
melting temperature of micro-capsulexe2x89xa6hardening temperature of binder resin; 
and
activation temperature of chelating agentxe2x89xa6hardening temperature of binder resin, 
then, a larger number of the conductive adhesive agents can be selected optionally. The reason is as follows.
Since the melting temperature of the micro-capsule is higher than the hardening temperature of the conductive adhesive agent, before the binder resin is hardened or when it is being hardened, the elution preventing film-forming agent does not form an elution preventing film on the conductive particle surfaces, thus providing good continuity. Then, when the binder resin is hardened and re-heated to a temperature higher than the melting temperature of the micro-capsule, an elution preventing film-forming is released from the micro-capsule to thereby form an elution preventing film only at a site not related to continuity. Accordingly, it is possible to more securely lower the connection resistance of the packaging structure after hardening. Also, it is not necessary to set the reaction temperature of the elution preventing film-forming agent at a temperature higher than the hardening temperature of the binder resin, a larger number of the elution preventing film-forming agents can be selected optionally.
Preferably the first and second methods uses such a conductive adhesive agent that the elution preventing film-forming agent is added to this conductive adhesive agent as dispersed in a non-polar solvent. Then, the following will occur.
Since the non-polar solvent serves to inhibit the reaction of the chelating agent, the elution preventing film-forming agent added to the conductive adhesive agent as dispersed in the non-polar solvent causes the chelating agent to be reactive little before the binder resin is hardened. Then, when the binder resin starts to be hardened, the chelating agent reacts with the conductive particle to form an elution preventing film containing a metallic complex. Accordingly, the elution preventing film (metallic complex) is formed further less before the binder resin is hardened, thus securely inhibiting a rise in the connection resistance in the conductive adhesive agent after being hardened. Further, since the activation temperature of the chelating agent may well be not higher than the application temperature of the conductive adhesive agent, the required properties (especially activation temperature) of the chelating agent come lenient, thus increasing the number of the chelating agents that can be used.
In the above-mentioned invention, the following materials can be used.
As the binder resin, almost all resins relatively easily available can be used. For example, as the thermo-hardening resin can be used epoxy resin, phenol resin, urea resin, melamine resin, furan resin, unsaturated-resin polyester resin, di-allyl phthalate resin, silicon resin, or the like. Also, as the thermo-hardening resin can be used vinyl chloride resin, vinylidene chloride resin, polystyrene resin, ionomer, methyl-penten resin, poly-allomer, fluorine resin, a poly-imide, poly-amide, poly-amide-imide, poly-carbonate, modified poly-phenylene oxide, poly-phenylene sulfide.
The micro-capsule may be made of such relatively easily available thermo-hardening resins as vinyl chloride resin, vinylidene chloride resin, polystyrene resin, ionomer, methyl-pentene resin, poly-allomer, fluorine resin, poly-amide, poly-imide, poly-amide-imide, poly-carbonate, modified poly-phenylene oxide, poly-phenylene sulfide, or the like. Note here that the melting temperature of the micro-capsule can be adjusted arbitrarily by adjusting the molar weight of the resin or the film thickness of the micro-capsule.
If the above-mentioned variety of requirements of the conductive adhesive agent and the packaging structure set by the invention are not satisfied, no object of the invention can be realized. The reason is described as follows.
If the melting point of the micro-capsule is not higher than the application temperature of the conductive adhesive agent, the micro-capsule melts before hardening, so that the elution preventing film-forming agent is released, thus forming an elution preventing film on the conductive particle surfaces, thus increasing the connection resistance of the packaging structure after hardening.
If the melting point of the micro-capsule is higher than the hardening temperature, the elution preventing film-forming agent does not react with the conductive particle even after hardening to thereby form no elution preventing film, thus failing to obtain the ion migration resistance nor the sulfurization resistance.
Also, if as the elution preventing film-forming agent added to the conductive adhesive agent is employed such an agent that has as its main component a chelating agent having an activation temperature higher than the hardening temperature (for example, bismthyol II having a melting point of 246xc2x0 C. as against a hardening temperature of 150xc2x0 C.), the elution preventing film-forming agent does not react with the conductive particle even after hardening to thereby form no elution preventing film, thus failing to obtain the ion migration resistance nor the sulfurization resistance.